[R-390] RE: The 26Z5W

[Drew Papanek]

Kenneth Arthur Crips wrote:

>This topic as got me wondering. It goes without saying keeping the power 
>supply in it's original configuration is the way to go.  But the Military 
>changed out the 26Z5W's with diodes.

The wording coursing through this list over the years regarding replacement 
of the 26Z5w's with silicon has gone something like "...virtually eliminates 
the possibility of a rectifier-based power supply failure..."  .  Greater 
reliability is the military's reason.

>I have been looking at solid state full wave rectifiers. These solid state 
>modules could be mounted >on a heat sink mounted on the power supply module 
>and would be a nice looking as well as very functional change.  One thing 
>you could do is to mount the full wave rectifiers on the heat sinks >which 
>are mounted on the CPU's in computers <snipped>

I assume you are referring to the full-wave 2 diode rectifiers in a TO-220 
like package.  A full wave bridge could also be used as a 2-diode type 
rectifier by simply not connecting the negative lead.  (Aside: works well as 
a replacement for defunct selenium  in car battery chargers and can be 
bolted to the charger's case for heatsinking.)

The rectifier current in the R-390( ) B+ supply results in negligible heat 
production in silicon rectifiers so applied.  No need for a heatsink.  
Regular diodes with leads can be soldered to the terminals of the orifinal 
rectifier sockets.

>Combine this with a solid state voltage regulator mounted in place of the 
>3TF7 I don't think you could >have a better setup.

A typical linear regulator used as a replacement for the 3TF7 does require a 
heatsink.   Some time ago David Wise developed a solid state regulator to 
replace the 3TF7 that did not require a heatsink.  It is a sophisticated 
microcontroller-based digital design.

Drew